Fish information

Bass biology and identification

Largemouth Bass: Dark green on top with silvery green to yellow green flanks and a cream belly, the largemouth bass is marked by a dark, irregular stripe along its side. The "maxilla," or upper jaw, extends rearward of the eye. The spiny and soft portions of the dorsal fin are separated by a deep notch. Anglers routinely catch bass between 1 and 2 pounds. In Minnesota, where bass grow more slowly than they do in the South, 6-pound bass are trophies.

dorsal fin example

The largemouth lives in lakes and streams throughout Minnesota- from the backwaters of the Mississippi, to isolated potholes along the Canadian border (where it may have been stocked). It is most abundant in the small to medium-size hard-water lakes of central, south-central, west-central and northwestern Minnesota. It is least common in the lakes of the Lake Superior drainage and the streams draining the southeastern hills.

Though the largemouth tolerates turbid water, it favors lakes with clear water, sandy shallows and abundant rooted aquatic weeds. It streams joining good bass lakes. The largemouth is a "warm-water" species. It flourishes in waters warmer than 80 degrees and can survive temperatures in the mid-90's.

The largemouth need water of 2 to 6 feet deep with firm sand, mud or gravel to spawn. As water temperatures near 60 degrees (between late April and early June) bass migrate from deep water toward these first and fans out a dish-shaped nest with its tail. As the water warms will lay from 2,000 to 7,000 eggs per pound of body weight. The male then fertilizes the eggs.

After spawning, the female moves off into deep water and does not feed for a couple of weeks. The male guards the nest until the eggs hatch and mature into a swarm of black fry. During this time, the male strikes savagely at intruding fish (or lures) but does not eat. It may even carry intruders and objects from the nest but then ejects them. When the fry reach an inch in length, they leave the nest. Then the male resumes feeding and in fact may eat any young bass he encounters.

Largely because of the male's fastidiousness in building and guarding the nest, many fry survive, and a few adult bass can quickly populate new waters. In fact, researchers have found no correlation between the number of spawning bass and the subsequent number of young-of-the-year fish. The success of the spawn depends entirely on good spawning areas and stable weather. A severe cold front, for example, may cause the male to desert the nest. Then the eggs or fry can be eaten by other fish.

As the water continues to warm after the spawn, largemouth spend much of their time in the shelter of thick cover or deeper water. During the summer, they typically feed in the shallows during evening and early morning.

Largemouth fingerling feed on increasingly large invertebrates and soon add small minnows to their diets. Adults eat minnows, yellow perch, sunfish and large invertebrates, such as crayfish and dragonfly nymphs, as well as any small terrestrial creature hapless enough to tumble into the water.

Largemouth feed largely by sight, but also use small and their ability to feel vibration through their "lateral line," a sense organ that runs longitudinally down their sides. In one experiment, researchers released minnows into a tank holding several largemouth bass that had been "blindfolded" with eye patches. The bass were able to locate the minnows through vibration alone and intercept them one by one.

Smallmouth Bass: Sometimes called a "bronzeback" for its brassy brown hue, the smallmouth differs from its cousin in several ways. Its mouth, though hardly small, is no match for the largemouth's; the maxilla extends rearward only about even with the pupil. The notch between the spiny and soft parts of the dorsal is less pronounced than the largemouth's. The smallmouth's marking consist of irregular vertical bars or a continuous shading of dark brown above to a gray or cream below. The average hook-and-line smallmouth ranges from « pound to 1 « pounds. A 5-pounder is exceptional.

The smallmouth is native to the Mississippi watershed. It is abundant throughout the limestone stream of the Root and Zumbro drainages that are too warm to support trout. It is found in the boulder tributaries of the Mississippi in central Minnesota (such as the Kettle and Snake). The Mississippi itself holds large smallmouth bass as far north as Brainerd. Farther north, river smallmouth become increasingly scarce, though they occupy stretches of the St. Louis, Cloquet and Whiteface rivers.

The smallmouth also is native to many central Minnesota lakes, through it is far less common in this environment than the largemouth. The keys to their presence in these waters are clear water and suitable spawning gravel and rubble.

During the late 1800's smallmouth were valued nearly as highly as trout and salmon and were transplanted to new watersheds with great fervor but little accurate record keeping. So biologist have been left to study historical records and postglacial drainage patterns to determine the presettlement range of the fish. Smallmouth bass probably are not native to the lakes that provide some of the best smallmouth fishing in the state, including Lake of the Woods, Rainy, Namakan, Vermillion and the large border lakes of the Boundary Waters Canoe Area Wilderness.

Though smallmouth flourish in many Minnesota lakes, they are primarily a creature of rivers. Whether smallmouth live in moving water or still, they are usually found next to rocks.. In particular, smallmouth prefer gravel from pea size to 1 inch in diameter to build their nests and spawn. Water temperatures must reach the low 60s for smallmouth bass to spawn, which is one reason many cold-water streams hold trout rather than bass. On the other hand, smallmouth shun waters that commonly exceed the mid-80s. Temperatures over 90 degrees are lethal. Smallmouth also need a great amount of dissolved oxygen and, in streams, a dependable streamflow and modest current.

In the spring bass disperse to their spawning areas in gravelly shallows of lakes or large, gentle eddies in streams. The male builds the nest. The female lays 2,000 to 10,000 eggs and then heads for deep water. The male remains on the nest two weeks or more, guarding eggs and fry.

As with the largemouth, research on smallmouth has shown no relationship between the number of spawning fish and the success of the spawn. The strength of the year class depends solely on water conditions - in particular, the absence of a sudden cold snap or muddy floodwaters that can kill eggs and fry.

Once the fry have left the nest, male and female bass resume feeding. In streams, the larger fish move between sheltering lies (usually in pools or near heavy cover) to feeding lies near current (such as eddies or riffles), where they feed on small fish and large invertebrates, especially crayfish. Lake fish feed in the shallows but spend more and more time in deep water as summer progresses.

Recent studies in northern latitudes have revealed that stream smallmouth may migrate much more than previously supposed. In the fall, as the water temperature drops below 60 degrees, smallmouth may migrate 50 miles or more, moving a dozen miles in a single day, to find their "hibernacula." These winter resting areas may be deep pools in a stream, or bass may desert a creek entirely, finding refuge in a larger river. There they crowd together and remain lethargic and eat little through the winter.